1. Field of the Invention
The present invention relates generally to digital display devices and more particularly to mechanical digital display devices having a plurality of transparent windows selectively shutterable by mechanical cam means.
2. Discussion of the Prior Art
Digital displays, or readouts, have found favor in many modern day applications as being among the most efficient means of quickly and accurately visually transmitting information. Everyday applications of visual displays include the light emitting diode or liquid crystal displays found in digital watches and calculators and the large light matrixes used for displaying scores at football, basketball and other sporting games.
The aforementioned digital display types are either electrical or electronic in nature. Another type of digital display device, particularly suited for large displays, is the mechanical or electro-mechanical digital display.
A couple of interesting mechanical digital displays are disclosed by Pirchl in U.S. Pat. No. 3,825,923, a first of which comprises an opaque face plate having a seven segment window formed thereon, behind which a visual surface having a series of vertical and transverse lines printed or otherwise fashioned on its surface is disposed and which may then be positioned under the seven segment windows to provide a seven segment display of digital numerals. A second type of visual display disclosed in the same patent comprises a plurality of flexible tongues which may be forced together by an externally situated cam to produce a digital readout.
Another mechanical digital display has an opaque face plate having seven segment or seven segment type windows behind which masks are moved relative to the faceplate, producing a patterned digital display when a light is shined through. An example of this type of device, disclosed by Trame in U.S. Pat. No. 4,021,944, uses a system of gears, eccentrics and slots to orbitally position a mask relative a face plate. Another example of this type of mechanical digital display, disclosed by Rinder in U.S. Pat. No. 3,399,475 has four masks independently moveable relative a face plate to provide a patterned digital display.
Another type of digital display device, disclosed by Vogt in U.S. Patent Application No. B493,981, has a number of geometrically-shaped screens which are moved by a cam and lever system across and about a background of contrasting color or shade.
While the digital displays found in the prior art admirably fulfill their function, they do possess a number of drawbacks. A common drawback of digital displays found in the prior art is that they are invariably mechanically complex, which, of course, leads to an increase in cost of the device and a greater chance for it to break down or otherwise malfunction. Furthermore, a number of the displays cannot show conventional digital or seven segment numerals due to various design considerations.
Another drawback with prior art digital displays is that they are not often directly actuable by rotary means, proving them of limited suitability for such purposes as digital clock displays.
Yet another disadvantage with digital displays found in the prior art is that they cannot always be back lighted, which would reduce their visibility in applications such as outdoor stadium display boards.